The present invention relates to an accelerometer capable of detecting small amounts of acceleration for all directions.
There has been known an accelerometer of a type in which the displacement of a pendulum caused by acceleration is adjusted back to its null position by a counterbalancing force exerted by the electrical spring of a servo mechanism, with the resultant feedback current being used to detect the applied acceleration. A problem with this type of accelerometer is that it is capable of detecting the displacement of the pendulum only in one direction so that in order to detect acceleration for all directions, a complex system including at least three units of accelerometer must be used.
A single unit of accelerometer, that is, designed to detect acceleration for all directions has been proposed in JP-A-59-5965 (the term "JPA" as used herein means an "unexamined published Japanese patent application"). In this accelerometer, the measurable force developed by a processing gyroscope is used. The device consists of an inner gimbal with a rapidly rotating off-balance mass and an outer gimbal in which the inner gimbal is mounted. Acceleration is measured by detecting the resulting movement of the outer gimbal relative to the inner gimbal.
Also known is an accelerometer of a type in which a magnet on a cylinder is fixed to a seismic mass, with another magnet being positioned inside the first magnet. acceleration is measured by detecting the resulting movement of the inner magnet relative to the outer magnet. An accelerometer of this type is described in JP-B-54-6226 (the term "JP-B" as used herein means an "examined Japanese patent publication").
A single unit of the accelerometer described in JP-A-59-5965 suffices for detecting acceleration for all directions but because of the friction between inner and outer gimbals, this device is not suitable for detecting small amounts of acceleration.
An accelerometer using the operating principle described in JP-B-54-6226 would be capable of frictionless support of the probe (or detection body) and hence has the potential to be used for detecting small amounts of acceleration. However, this accelerometer is not adapted for practical applications since the position of the probe is not subject to feedback control. In addition, precise detection of acceleration is impossible since the probe which might be displaced by gravity or some other disturbing factors cannot be adjusted to a predetermined position by feedback control.